Open ones anyone can access to. Like Rutracker.
Private ones you need to have an account to log in, and usually to get an account you need to be referred by someone who has an account as well. So you can't just join there, but need to know people.
Private tracker pros tend to be some turbo burgers who got immensely butthurt over the fact that most people don't seed, so they created their own tracker from where they can ban people who don't seed enough.
It's cringe. Leeching is not nearly as big of an issue as these private burgers make it out to be.
Data should be public, accessible to everyone and seeding it be voluntary. Has worked on public trackers for decades just fine.
If you are paranoid about the cops, use a VPN. It's not like private trackers are ultra secure either. If the cops are really out to get you, private trackers help very little, and if they are just copying random IPs they found on the seedlist, and aren't super motivated to truly get you beyond that, VPN is enough.